Managing secondary cell connections in unlicensed spectrum

ABSTRACT

In wireless communication networks using carrier aggregation including a secondary component carrier in unlicensed spectrum, a user equipment (UE) may monitor a downlink radio link quality of secondary cells for an event indicating failure of a communication link in the unlicensed spectrum with a secondary cell. The UE detects one or more failure events based on the downlink radio link quality. When a designated set of failure events is detected, the UE declares a failure state on the secondary cell. In response to the failure state, the UE may adjust operations related to the secondary component carrier in the unlicensed spectrum in order to save power and resources.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims priority to ProvisionalApplication No. 62/357,246 entitled “MANAGING SECONDARY CELL CONNECTIONSIN UNLICENSED SPECTRUM” filed Jun. 30, 2016, which is assigned to theassignee hereof, and incorporated herein by reference in its entirety.

BACKGROUND Field

Aspects of the present disclosure relate generally to wirelesscommunication systems, and more particularly, to managing secondary cellconnections.

Background

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, and the like. These wireless networks may be multiple-accessnetworks capable of supporting multiple users by sharing the availablenetwork resources. Such networks, which are usually multiple accessnetworks, support communications for multiple users by sharing theavailable network resources. One example of such a network is theUniversal Terrestrial Radio Access Network (UTRAN). The UTRAN is theradio access network (RAN) defined as a part of the Universal MobileTelecommunications System (UMTS), a third generation (3G) mobile phonetechnology supported by the 3rd Generation Partnership Project (3GPP).Examples of multiple-access network formats include Code DivisionMultiple Access (CDMA) networks, Time Division Multiple Access (TDMA)networks, Frequency Division Multiple Access (FDMA) networks, OrthogonalFDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.

A wireless communication network may include a number of base stationsor node Bs that can support communication for a number of userequipments (UEs). A UE may communicate with a base station via downlinkand uplink. The downlink (or forward link) refers to the communicationlink from the base station to the UE, and the uplink (or reverse link)refers to the communication link from the UE to the base station.

A base station may transmit data and control information on the downlinkto a UE and/or may receive data and control information on the uplinkfrom the UE. On the downlink, a transmission from the base station mayencounter interference due to transmissions from neighbor base stationsor from other wireless radio frequency (RF) transmitters. On the uplink,a transmission from the UE may encounter interference from uplinktransmissions of other UEs communicating with the neighbor base stationsor from other wireless RF transmitters. This interference may degradeperformance on both the downlink and uplink.

As the demand for mobile broadband access continues to increase, thepossibilities of interference and congested networks grows with more UEsaccessing the long-range wireless communication networks and moreshort-range wireless systems being deployed in communities. Research anddevelopment continue to advance the UMTS technologies not only to meetthe growing demand for mobile broadband access, but to advance andenhance the user experience with mobile communications.

SUMMARY

The following disclosure presents a simplified summary of one or moreaspects in order to provide a basic understanding of such aspects. Thissummary is not an extensive overview of all contemplated aspects, and isintended to neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

In one aspect of the disclosure, a method for wireless communication ona secondary component carrier in an unlicensed spectrum in a wirelesscommunication network using carrier aggregation is provided. The methodincludes monitoring a downlink radio link quality of one or moreconfigured secondary cells operating in the unlicensed spectrum at amobile device for an event indicating failure of a communication linkwith at least one of the configured secondary cells. The method mayinclude detecting a first event based on the downlink radio linkquality. The method may include declaring a failure state on the atleast one of the configured secondary cells in response to detecting thefirst event, during which the mobile device adjusts operation related tothe secondary component carrier in the unlicensed spectrum.

An additional aspect of the present disclosure is directed to anapparatus for wireless communication on a secondary component carrier inan unlicensed spectrum in a wireless communication network using carrieraggregation. The apparatus may include means for monitoring a downlinkradio link quality of one or more configured secondary cells operatingin the unlicensed spectrum at a mobile device for an event indicatingfailure of a communication link with at least one of the configuredsecondary cells. The apparatus may include means for detecting a firstevent based on the downlink radio link quality. The apparatus mayinclude means for declaring a failure state on the at least one of theconfigured secondary cells in response to detecting the first event,during which the mobile device adjusts operation related to thesecondary component carrier in the unlicensed spectrum.

An additional aspect of the present disclosure is directed to anon-transitory computer-readable medium having computer executable codestored thereon. The code includes code for causing a computer to monitora downlink radio link quality of one or more secondary cells operatingin an unlicensed spectrum at a mobile device for an event indicatingfailure of a communication link with at least one of the configuredsecondary cells. The code may include code for causing the computer todetect a first event based on the downlink radio link quality. The codemay include code for causing the computer to declare a failure state onthe at least one of the configured secondary cells in response todetecting the first event, during which the mobile device adjustsoperation related to the secondary component carrier in the unlicensedspectrum.

An additional aspect of the present disclosure is directed to anapparatus configured for wireless communication. The apparatus includesat least one processor and a memory coupled to the processor. Theprocessor may be configured to monitor a downlink radio link quality ofone or more secondary cells operating in the unlicensed spectrum at amobile device for an event indicating failure of a communication linkwith at least one of the configured secondary cells. The processor maybe configured to detect a first event based on the downlink radio linkquality. The processor may be configured to declare a failure state onthe at least one of the configured secondary cells in response todetecting the first event, during which mobile device adjusts operationrelated to the secondary component carrier in the unlicensed spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of amobile communication system.

FIG. 2 is a block diagram conceptually illustrating a design of a basestation/eNB and a UE configured according to one aspect of the presentdisclosure.

FIG. 3 is a block diagram illustrating a wireless network configuredaccording to aspects of the present disclosure.

FIG. 4 is a functional block diagram illustrating example blocksexecuted to implement aspects of the present disclosure.

FIG. 5 is a timing diagram illustrating a UE configured according toaspects of the present disclosure.

FIG. 6 is a block diagram illustrating a UE configured according toaspects of the present disclosure.

FIG. 7 is a block diagram illustrating a UE including a radio linkstatus component configured according to aspects of the presentdisclosure.

FIG. 8 illustrates an example of carrier aggregation using a componentcarrier in unlicensed spectrum according to aspects of the presentdisclosure.

FIG. 9 illustrates an example of carrier sense adaptive transmission(CSAT) for use in unlicensed spectrum according to aspects of thepresent disclosure.

FIG. 10 illustrates an example of an enhanced CSAT (eCSAT) system thatmay operate without a clear channel assessment (CCA) or listen beforetalk (LBT) procedure according to aspects of the present disclosure.

FIG. 11 illustrates an example of eCSAT operation with a CCA or LBTprocedure according to aspects of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to limit the scope of the disclosure.Rather, the detailed description includes specific details for thepurpose of providing a thorough understanding of the inventive subjectmatter. It will be apparent to those skilled in the art that thesespecific details are not required in every case and that, in someinstances, well-known structures and components are shown in blockdiagram form for clarity of presentation.

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology, suchas Universal Terrestrial Radio Access (UTRA), TelecommunicationsIndustry Association's (TIA's) CDMA2000®, and the like. The UTRAtechnology includes Wideband CDMA (WCDMA) and other variants of CDMA.The CDMA2000® technology includes the IS-2000, IS-95 and IS-856standards from the Electronics Industry Alliance (EIA) and TIA. A TDMAnetwork may implement a radio technology, such as Global System forMobile Communications (GSM). An OFDMA network may implement a radiotechnology, such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB),IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, andthe like. The UTRA and E-UTRA technologies are part of Universal MobileTelecommunication System (UMTS). 3GPP Long Term Evolution (LTE) andLTE-Advanced (LTE-A) are newer releases of the UMTS that use E-UTRA.UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents froman organization called the “3rd Generation Partnership Project” (3GPP).CDMA2000® and UMB are described in documents from an organization calledthe “3rd Generation Partnership Project 2” (3GPP2). The techniquesdescribed herein may be used for the wireless networks and radio accesstechnologies mentioned above, as well as other wireless networks andradio access technologies. For clarity, certain aspects of thetechniques are described below for LTE or LTE-A (together referred to inthe alternative as “LTE/-A”) and use such LTE/-A terminology in much ofthe description below.

In some systems, LTE in unlicensed spectrum may be employed in astandalone configuration, with all carriers operating exclusively in anunlicensed portion of the wireless spectrum (e.g., LTE Standalone). Inother systems, LTE in unlicensed spectrum may be employed in a mannerthat is supplemental to licensed band operation by providing one or moreunlicensed carriers operating in the unlicensed portion of the wirelessspectrum in conjunction with an anchor licensed carrier operating in thelicensed portion of the wireless spectrum (e.g., LTE SupplementalDownLink (SDL)). In either case, carrier aggregation may be employed tomanage the different component carriers, with one carrier serving as thePrimary Cell (PCell) for the corresponding UE (e.g., an anchor licensedcarrier in LTE SDL or a designated one of the unlicensed carriers in LTEStandalone) and the remaining carriers serving as respective SecondaryCells (SCells). In this way, the PCell may provide an FDD paireddownlink and uplink (licensed or unlicensed), and each SCell may provideadditional downlink capacity as desired. Additionally, unlicensedspectrum may also be referred to as a shared spectrum. In an aspect, anunlicensed spectrum may refer to a spectrum in which multiple devicesgain access to a medium by contention-based operations.

FIG. 1 shows a wireless network 100 for communication, which may be anLTE-A network operating at least in part in an unlicensed spectrum. Thewireless network 100 includes a number of evolved node Bs (eNBs) 110 andother network entities. An eNB may be a station that communicates withthe UEs and may also be referred to as a base station, a node B, anaccess point, and the like. Each eNB 110 may provide communicationcoverage for a particular geographic area. In 3GPP, the term “cell” canrefer to this particular geographic coverage area of an eNB and/or aneNB subsystem serving the coverage area, depending on the context inwhich the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell generally coversa relatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscriptions withthe network provider. A pico cell would generally cover a relativelysmaller geographic area and may allow unrestricted access by UEs withservice subscriptions with the network provider. A femto cell would alsogenerally cover a relatively small geographic area (e.g., a home) and,in addition to unrestricted access, may also provide restricted accessby UEs having an association with the femto cell (e.g., UEs in a closedsubscriber group (CSG), UEs for users in the home, and the like). An eNBfor a macro cell may be referred to as a macro eNB. An eNB for a picocell may be referred to as a pico eNB. And, an eNB for a femto cell maybe referred to as a femto eNB or a home eNB. In the example shown inFIG. 1, the eNBs 110 a, 110 b and 110 c are macro eNBs for the macrocells 102 a, 102 b and 102 c, respectively. The eNB 110 x is a pico eNBfor a pico cell 102 x, serving a UE 120 x. And, the eNBs 110 y and 110 zare femto eNBs for the femto cells 102 y and 102 z, respectively. An eNBmay support one or multiple (e.g., two, three, four, and the like)cells.

The wireless network 100 may also include relay stations. A relaystation is a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., an eNB, a UE, or the like)and sends a transmission of the data and/or other information to adownstream station (e.g., another UE, another eNB, or the like). A relaystation may also be a UE that relays transmissions for other UEs. In theexample shown in FIG. 1, a relay station 110 r may communicate with theeNB 110 a and a UE 120 r, in which the relay station 110 r acts as arelay between the two network elements (the eNB 110 a and the UE 120 r)in order to facilitate communication between them. A relay station mayalso be referred to as a relay eNB, a relay, and the like.

The wireless network 100 may support synchronous or asynchronousoperation. For synchronous operation, the eNBs may have similar frametiming, and transmissions from different eNBs may be approximatelyaligned in time. For asynchronous operation, the eNBs may have differentframe timing, and transmissions from different eNBs may not be alignedin time.

The UEs 120 are dispersed throughout the wireless network 100, and eachUE may be stationary or mobile. A UE may also be referred to as aterminal, a mobile station, a subscriber unit, a station, or the like. AUE may be a cellular phone, a smart phone, a personal digital assistant(PDA), a wireless modem, a wireless communication device, a handhelddevice, a tablet computer, a laptop computer, a cordless phone, awireless local loop (WLL) station, or the like. A UE may be able tocommunicate with macro eNBs, pico eNBs, femto eNBs, relays, and thelike. In FIG. 1, a solid line with double arrows indicates desiredtransmissions between a UE and a serving eNB, which is an eNB designatedto serve the UE on the downlink and/or uplink. A dashed line with doublearrows indicates interfering transmissions between a UE and an eNB.

LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition the system bandwidth into multiple(K) orthogonal subcarriers, which are also commonly referred to astones, bins, or the like. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (K) may bedependent on the system bandwidth. For example, K may be equal to 72,180, 300, 600, 900, and 1200 for a corresponding system bandwidth of1.4, 3, 5, 10, 15, or 20 megahertz (MHz), respectively. The systembandwidth may also be partitioned into sub-bands. For example, asub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bandsfor a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 MHz,respectively.

In LTE/-A, an eNB may send a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) for each cell in the eNB. The eNBmay send the PSS, SSS and Physical Broadcast Channel (PBCH) in thecenter 1.08 MHz of the system bandwidth used by the eNB. The eNB maysend the Physical Control Format Indicator Channel (PCFICH) and PhysicalHybrid Automatic Repeat Request (HARD) Indicator Channel (PHICH) acrossthe entire system bandwidth in each symbol period in which thesechannels are sent. The eNB may send the Physical Downlink ControlChannel (PDCCH) to groups of UEs in certain portions of the systembandwidth. The eNB may send the Physical Downlink Shared Channel (PDSCH)to specific UEs in specific portions of the system bandwidth. The eNBmay send the PSS, SSS, PBCH, PCFICH and PHICH in a broadcast manner toall UEs, may send the PDCCH in a unicast manner to specific UEs, and mayalso send the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period.Each resource element may cover one subcarrier in one symbol period andmay be used to send one modulation symbol, which may be a real orcomplex value. Resource elements not used for a reference signal in eachsymbol period may be arranged into resource element groups (REGs). EachREG may include four resource elements in one symbol period. The PCFICHmay occupy four REGs, which may be spaced approximately equally acrossfrequency, in symbol period 0. The PHICH may occupy three REGs, whichmay be spread across frequency, in one or more configurable symbolperiods. For example, the three REGs for the PHICH may all belong insymbol period 0 or may be spread in symbol periods 0, 1 and 2. The PDCCHmay occupy 9, 18, 32 or 64 REGs, which may be selected from theavailable REGs, in the first M symbol periods. Only certain combinationsof REGs may be allowed for the PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. TheUE may search different combinations of REGs for the PDCCH. The numberof combinations to search is typically less than the number of allowedcombinations for the PDCCH. An eNB may send the PDCCH to the UE in anyof the combinations that the UE will search.

A UE may be within the coverage of multiple eNBs. One of these eNBs maybe selected to serve the UE. The serving eNB may be selected based onvarious criteria such as received power, path loss, signal-to-noiseratio (SNR), etc.

The wireless network 100 uses the diverse set of eNBs 110 (i.e., macroeNBs, pico eNBs, femto eNBs, and relays) to improve the spectralefficiency of the system per unit area. Because the wireless network 100uses such different eNBs for its spectral coverage, it may also bereferred to as a heterogeneous network. The macro eNBs 110 a-c areusually carefully planned and placed by the provider of the wirelessnetwork 100. The macro eNBs 110 a-c generally transmit at high powerlevels (e.g., 5 W-40 W). The pico eNB 110 x and the relay station 110 r,which generally transmit at substantially lower power levels (e.g., 100mW-2 W), may be deployed in a relatively unplanned manner to eliminatecoverage holes in the coverage area provided by the macro eNBs 110 a-cand improve capacity in the hot spots. The femto eNBs 110 y-z, which aretypically deployed independently from the wireless network 100 may,nonetheless, be incorporated into the coverage area of the wirelessnetwork 100 either as a potential access point to the wireless network100, if authorized by their administrator(s), or at least as an activeand aware eNB that may communicate with the other eNBs 110 of thewireless network 100 to perform resource coordination and coordinationof interference management. The femto eNBs 110 y-z typically alsotransmit at substantially lower power levels (e.g., 100 mW-2 W) than themacro eNBs 110 a-c.

In operation of a heterogeneous network, such as the wireless network100, each UE is usually served by the eNB 110 with the better signalquality, while the unwanted signals received from the other eNBs 110 aretreated as interference. While such operational principals can lead tosignificantly sub-optimal performance, gains in network performance arerealized in the wireless network 100 by using intelligent resourcecoordination among the eNBs 110, better server selection strategies, andmore advanced techniques for efficient interference management.

In deployments of heterogeneous networks, such as the wireless network100, a UE may operate in a dominant interference scenario in which theUE may observe high interference from one or more interfering eNBs. Adominant interference scenario may occur due to restricted association.For example, in FIG. 1, the UE 120 y may be close to the femto eNB 110 yand may have high received power for the eNB 110 y. However, the UE 120y may not be able to access the femto eNB 110 y due to restrictedassociation and may then connect to the macro eNB 110 c (as shown inFIG. 1) or to the femto eNB 110 z also with lower received power (notshown in FIG. 1). The UE 120 y may then observe high interference fromthe femto eNB 110 y on the downlink and may also cause high interferenceto the eNB 110 y on the uplink. Using coordinated interferencemanagement, the eNB 110 c and the femto eNB 110 y may communicate overthe backhaul 134 to negotiate resources. In the negotiation, the femtoeNB 110 y agrees to cease transmission on one of its channel resources,such that the UE 120 y will not experience as much interference from thefemto eNB 110 y as it communicates with the eNB 110 c over that samechannel.

FIG. 2 shows a block diagram of a design of a base station/eNB 110 and aUE 120, which may be one of the base stations/eNBs and one of the UEs inFIG. 1. For a restricted association scenario, the eNB 110 may be themacro eNB 110 c in FIG. 1, and the UE 120 may be the UE 120 y. The eNB110 may also be a base station of some other type. The eNB 110 may beequipped with antennas 234 a through 234 t, and the UE 120 may beequipped with antennas 252 a through 252 r.

At the eNB 110, a transmit processor 220 may receive data from a datasource 212 and control information from a controller/processor 240. Thecontrol information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. Thedata may be for the PDSCH, etc. The transmit processor 220 may process(e.g., encode and symbol map) the data and control information to obtaindata symbols and control symbols, respectively. The transmit processor220 may also generate reference symbols, e.g., for the PSS, SSS, andcell-specific reference signal. A transmit (TX) multiple-inputmultiple-output (MIMO) processor 230 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, and/or thereference symbols, if applicable, and may provide output symbol streamsto the modulators (MODs) 232 a through 232 t. Each modulator 232 mayprocess a respective output symbol stream (e.g., for OFDM, etc.) toobtain an output sample stream. Each modulator 232 may further process(e.g., convert to analog, amplify, filter, and upconvert) the outputsample stream to obtain a downlink signal. Downlink signals frommodulators 232 a through 232 t may be transmitted via the antennas 234 athrough 234 t, respectively.

At the UE 120, the antennas 252 a through 252 r may receive the downlinksignals from the eNB 110 and may provide received signals to thedemodulators (DEMODs) 254 a through 254 r, respectively. Eachdemodulator 254 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 254 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 256 may obtainreceived symbols from all the demodulators 254 a through 254 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 258 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forthe UE 120 to a data sink 260, and provide decoded control informationto a controller/processor 280.

On the uplink, at the UE 120, a transmit processor 264 may receive andprocess data (e.g., for the PUSCH) from a data source 262 and controlinformation (e.g., for the PUCCH) from the controller/processor 280. Thetransmit processor 264 may also generate reference symbols for areference signal. The symbols from the transmit processor 264 may beprecoded by a TX MIMO processor 266 if applicable, further processed bythe modulators 254 a through 254 r (e.g., for SC-FDM, etc.), andtransmitted to the eNB 110. At the eNB 110, the uplink signals from theUE 120 may be received by the antennas 234, processed by thedemodulators 232, detected by a MIMO detector 236 if applicable, andfurther processed by a receive processor 238 to obtain decoded data andcontrol information sent by the UE 120. The processor 238 may providethe decoded data to a data sink 239 and the decoded control informationto the controller/processor 240.

The controllers/processors 240 and 280 may direct the operation at theeNB 110 and the UE 120, respectively. The controller/processor 240and/or other processors and modules at the eNB 110 may perform or directthe execution of various processes for the techniques described herein.The controllers/processor 280 and/or other processors and modules at theUE 120 may also perform or direct the execution of the functional blocksillustrated in FIG. 4, and/or other processes for the techniquesdescribed herein. The memories 242 and 282 may store data and programcodes for the eNB 110 and the UE 120, respectively. A scheduler 244 mayschedule UEs for data transmission on the downlink and/or uplink.

LTE-A UEs use spectrum up to 20 MHz bandwidths allocated in a carrieraggregation of up to a total of 100 MHz (5 component carriers) used fortransmission in each direction. Generally, less traffic is transmittedon the uplink than the downlink, so the uplink spectrum allocation maybe smaller than the downlink allocation. For example, if 20 MHz isassigned to the uplink, the downlink may be assigned 100 MHz. Theseasymmetric FDD assignments will conserve spectrum and are a good fit forthe typically asymmetric bandwidth utilization by broadband subscribers.

For the LTE-A mobile systems, two types of carrier aggregation (CA)methods have been proposed, continuous CA and non-continuous CA.Non-continuous CA occurs when multiple available component carriers areseparated along the frequency band. On the other hand, continuous CAoccurs when multiple available component carriers are adjacent to eachother. Both non-continuous and continuous CA aggregate multipleLTE/component carriers to serve a single unit of LTE-A UE.

According to various aspects, a UE operating in CA may be configured toaggregate certain functions of multiple carriers, such as control andfeedback functions, on the same carrier, which may be referred to as“primary component carriers.” The network entities, eNBs, access points,and the like that communicate with a UE using the primary componentcarriers are referred to as “primary cells” or “PCells.” The remainingcarriers that depend on the primary carrier for support are referred toas “secondary component carriers.” The network entities, eNBs, accesspoints, and the like that communicate with a UE using the secondarycomponent carriers are referred to as “secondary cells” or “SCells.” Forexample, the UE may aggregate control functions such as those providedby the optional dedicated channel (DCH), the nonscheduled grants, aphysical uplink control channel (PUCCH), and/or a physical downlinkcontrol channel (PDCCH). Signaling and payload may be transmitted bothon the downlink by the eNB to the UE, and on the uplink by the UE to theeNB.

In cellular networks, in particular LTE networks, UEs are expected tomonitor the quality of the radio link of the primary cell's receivedsignal. The purpose of radio link monitoring (RLM) in the UE is tomonitor the downlink radio link quality of the primary serving cell in aconnected state and may be based on the cell specific reference signals(RSs). This, in turn, may enable the UE, when in a connected state, todetermine whether the UE is in-sync or out-of-sync with respect to theUE's primary serving cell. In operation, counters may be used to countthe consecutive in-sync and out-of-sync indicators, respectively. Incase of a the consecutive primary cell out-of-sync counter exceeding acertain number or threshold value, the UE may start a network-configuredradio link failure timer. The timer may be stopped prior to expirationif the consecutive in-sync counter records a certain number ofconsecutive in-sync indications reported by the UE' s physical layer.Both the out-of-sync and in-sync counters are typically configured bythe network. Upon expiry of the timer, without being stopped by thein-sync counter, Radio Link Failure (RLF) occurs at the UE and,consequently, the UE may start a re-establishment procedure toreestablish the radio communication link.

The UE's estimate of the downlink radio link quality may be comparedwith out-of-sync and in-sync thresholds for the purpose of RLM. Theout-of-sync and in-sync thresholds may be expressed in terms of a BlockError Rate (BLER) of a hypothetical PDCCH transmission from the servingcell. The out-of-sync threshold may correspond to a 10% BLER while thein-sync threshold may correspond to a 2% BLER. The same threshold levelsmay be applicable with and without discontinuous reception (DRX). Themapping between the cell specific RS-based downlink quality and thehypothetical PDCCH BLER may be a UE implementation design choice.

In the case of carrier aggregation, RLM requirements may only apply tothe primary cell and the UE may not perform RLM monitoring of thesecondary cells. In other words, when the UE is configured withsecondary cells, it may use the primary cell to detect the downlinkradio link quality, and for sending out-of-sync/in-sync indications tohigher layers. The eNB may determine radio link quality of the secondarycells via a channel quality indicator (CQI) or other such measurementreports.

A UE may operate a demodulation path that includes time/frequencytracking loops that can correct up to a certain amount of time orfrequency shift due to multi-path or Doppler shift effect. Thesetracking loops generally have limited corrective capabilities and may beinitialized at the start time of the connection with the associatedsecondary cell. Without proper initialization, (1) the tracking loopsmay not converge, or (2) the convergence time may be as high as tens ofmilliseconds to a few hundreds of milliseconds, which may be many timeshigher than the typical subframe duration (e.g., 1 ms for LTE).

In the context of carrier aggregation the following situations can occurwhen a UE is configured with one or more secondary cells: (1) Asecondary cell may be activated for a UE when the UE is outside thesecondary cell range (or coverage area) and then, moves into thesecondary cell range sometime after the activation; (2) A UE temporarilymoves out of a secondary cell range and then moves back into the rangeof the secondary cell when the primary cell/secondary cell timingdifference is substantially different from the time where the UE leftthe secondary cell range (e.g., theoretically up to 62.6 μs, consideringthe LTE specifications allow for up to 31.3 μs PCell/SCell timingdifference), such as, for example, when remote-radio-heads (RRH) areused for secondary cell coverage extensions, etc.; and (3) A secondarycell's RF chain may be relinquished in order to be used to accessanother wireless technology (opportunistic CA) and is given back to theLTE stack after a long duration of time. For example, a secondary cell'sRF chain and demodulation path may be used to tune to the frequency of acell of another technology (e.g., Simultaneous Voice LTE (SV-LTE), DualSIM, Dual-Active (DSDA) technologies, etc.). In operation, the UE maystop monitoring the secondary cell to answer another technology call,such as a circuit switched call on a 1x system, and then, sometimelater, return to monitoring the secondary cell.

Without active management of the connections with the SCells, during thetime that the UE is out of SCell coverage and/or is not able to tracktime/frequency of the SCell, the state of the tracking loops may becomeobsolete and may de-converge to random states. Therefore, it may becomeimpossible for the tracking loops to re-converge or the convergence timemay become too long once the UE returns to the SCell coverage area. Thiscan be important with respect to time offset of the time tracking loopas the time offset variations between PCell and SCell may be up to 31.3μs.

When a secondary cell is operating in an unlicensed spectrum,communications may be subject to clear channel assessment (CCA). Forexample, a secondary cell may mute a transmission when it detectsanother radio transmission using the unlicensed spectrum. In an aspect,some metrics of secondary cell performance may be affected by thesecondary cell muting transmissions. For example, from the perspectiveof a UE, it is difficult to tell the difference between a transmissionin a sub-frame from the secondary cell with a low transmission power anda sub-frame where the secondary cell has muted the transmission.Accordingly, a metric such as a block error rate or SNR may bemisleading. For example, a high block error rate or low SNR may occurwhen the secondary cell is muting transmissions even though the UE maybe capable of receiving a signal from the secondary cell when thesecondary cell does transmit. In another aspect, a UE may attempt todetermine whether the secondary cell transmitted in a sub-frame bymonitoring a cell specific reference signal (CRS). If the UE does notdetect a CRS in a sub-frame, the UE may exclude the sub-frame fromanother measurement such as BLER or SNR. However, because it isdifficult to determine whether the sub-frame was muted or the radio linkwas poor quality, excluding the sub-frame may artificially boost somemetrics.

Various aspects of the present disclosure provide for monitoring of thelink quality between the UE and SCells operating in unlicensed spectrumto detect a failure event. For example, a failure event may include theUE going out of range of an SCell or an SCell being substantiallyblocked from transmitting by another system. The UE may detect a failureevent when a high number of search failures are detected, a low numberof non-muted sub-frames are received, no indications of suitable radiolink quality are reported, or no acceptable SNR is measured for a timeperiod. When such a failure event is detected, the UE may declare afailure state for the connection with the SCell associated with thefailure event. In declaring the failure state, the UE is determining foritself the failed state. For purposes of this application, the UEdeclaring the failure state with the SCell does not include signalingany network entity outside of the UE that such failure has occurred. Thedeclared failure state is internal to the UE. Based on this failurestate, the UE may adjust operations, such as by suspending ordeactivating certain components/modules and/or operations associatedwith the connection to the SCells, modifying the radio frequency (RF)chip state (e.g., disabling the RF chip or placing the RF chip in alower power mode; disabling transmission while keeping receptionenabled, etc.), suspending the transmit and receive paths for the SCell,reducing the power or voltage levels of the device components, changingmemory usage or operating frequency of certain device components, andthe like. When such failure state is declared, the UE may reduceresource consumption when certain resources associated with maintainingthe connection to the associated SCell are not needed.

Also in response to declaring the failure state, the UE may begin a cellsearch for the SCell. The cell search may be a narrowband search thatmonitors for PSS/SSS of the SCell. When the SCell is detected, the UEmay use the results of the search to recover or restore the connectionor communication link with the SCell. The connection is recovered orrestored when the UE is able to establish communication with thedetected SCell to a quality level that decoding may occur of datareceived via the SCell. In some circumstances, the SCell recovered orrestored may be the same SCell associated with the failure event. Inother circumstances, the SCell recovered may, in fact, be a new SCellthat was activated when the UE was out of range of that SCell's coveragearea. The UE may use the results from the search to initialize orre-initialize the time/frequency tracking loops of the recovered SCell.

FIG. 3 is a block diagram illustrating a wireless network 30 serving aUE 300 configured according to one aspect of the present disclosure andincluding a radio link status component 330. The UE 300 may be anexample of a UE 120 in FIG. 1 and FIG. 2. The radio link statuscomponent 330 may perform radio link monitoring operations at the UE300. In particular, the radio link status component 330 may monitor theradio link between the UE 300 and an SCell. The radio link statuscomponent 330 may include a monitoring component 332 for monitoring adownlink radio link quality of a SCell in unlicensed spectrum, ananalysis component 334 for detecting a first event based on the downlinkradio link quality, a failure state component 336 for declaring afailure state of the secondary cell in response to detecting the firstevent, and a link recovery component 338 for recovering from a failurestate.

At time, t1, UE 300 is in communication with eNB 301, within coveragearea 31, and remote radio head (RRH) 302, within coverage area 32.Wireless network 30 is configured to use carrier aggregation. UE 300communicates using the primary component carrier through the PCell, eNB301. Wireless network 30 assigns and activates RRH 302 to communicateover the secondary component carrier as an SCell to UE 300. At time, t1,UE 300 is communicating with the PCell eNB 301 and is also decodingcommunication on the secondary component carrier from SCell RRH 302.Also at time, t1, wireless network 30 assigns and activates access point303 as an SCell for UE 300. UE 300 may or may not be informed of thisassignment of access point 303. However, at time, t1, UE 300 is notwithin coverage area 33 of access point 303. Thus, as UE 300 fails todetect access point 303, it reports this failure to wireless network 30through PCell eNB 301, such as through a low or 0 CQI or out-of-rangeCQI indication and/or a low value for a rank indicator. In an aspect,however, the failure to detect access point 303 may also be due to theaccess point 303 muting sub-frames for carrier sense adaptivetransmission (CSAT). Further details of CSAT are provided below inconnection with FIGS. 9-11. Accordingly, a single determination ortransmission of a low or 0 CQI or out-of-range QCI indication and/or lowvalue for a rank indicator may not be indicative of overall linkquality. Accordingly, the UE 300 may monitor the determined CQI valuesfor repeated 0 CQI or out-of-range CQI indication and/or low values forthe rank indicator. Conversely, the UE may monitor for a non-zero CQIduring a time period to determine that no failure has occurred.

At time, t2, UE 300 has traveled into coverage area 33 of SCell accesspoint 303 and out of coverage area 32 of SCell RRH 302. UE 300 monitorsthe link quality of the connection or communication link with SCell RRH302. When a failure event is detected, UE 300 declares for itself afailure state with SCell RRH 302. This failure event may be detected byperiodically performing a narrowband cell search for the SCell RRH 302,counting non-muted subframes from the SCell RRH 302 within a timeperiod, monitoring determined CQI values for the SCell RRH 302 during atime period, or monitoring an SNR metric associated with the SCell, suchas SCell RRH 302. In response to the failure state, UE 300 may modifyoperations by suspending or deactivating certain components and/oroperations associated with the connection to SCell RRH 302, such asreducing power to the receive and transmit paths, suspending thedemodulation path with SCell RRH 302, and the like. UE 300 may alsobegin a cell search for SCell RRH 302 in response to the failure statebeing declared.

Regarding SCell access point 303, access point 303 may be activated bywireless network 30 as an SCell for UE 300 at time, t1. However, uponactivation of SCell access point 303, UE 300 may not be within coveragearea 33 of SCell access point 303. When UE 300 enters coverage area 33of SCell access point 303, UE 300 may begin to detect the PSS/SSS ofSCell access point 303 in a cell search. UE 300 may then initialize thetime/frequency tracking loops and establish a connection with SCellaccess point 303 at time, t2. Once the connection is established, UE 300may unsuspend or activate the components and/or operations that wereassociated with the connection of SCell RRH 302 and may begin reportinga CQI to wireless network 30 for SCell access point 303, after whichwireless network 30 may begin transmitting data to UE 300 over thesecondary component carrier through SCell access point 303, thus,providing additional bandwidth to UE 300.

It should be noted that SCell access point 303 may be detected duringthe cell search that begins when the failure state is declared on thefailure of the connection with SCell RRH 302 or during any periodic cellsearch. In such case of detecting a new secondary cell, UE 300 maycompare the time/frequency offset data recovered from the cell searchagainst the prior time/frequency offset data maintained by the previoustime/frequency tracking loops associated with SCell RRH 302. Duringnormal connection with a secondary cell, a UE may monitor thetime/frequency offset data associated with the time/frequency trackingloops. The UE may maintain this time/frequency offset data when theconnection is lost and this offset data will be compared against thesearch values of time/frequency offsets when the secondary cell is againdetected. If the difference between the previous value of time/frequencyoffsets and the search values is small or, at least within the pull-inrange of the time/frequency tracking loop, then the tracking loops maynot be re-initialized. However, when offset values are out-of-sync by anamount outside of the pull-in range of the tracking loops, UE 300 mayrepopulate the time/frequency offset data to the tracking loops usingthe offset data resulting from the cell search.

At time, t3, UE 300 may move back into coverage area 32 of SCell RRH302, while staying within coverage areas 32 and 31 of SCell access point303 and PCell eNB 301, respectively. UE 300 may continue searching foravailable SCells. As UE 300 initially re-enters coverage area 32 ofSCell RRH 302, the cell search will detect the PSS/SSS from SCell RRH302 and, when the signal quality of the reference signals from SCell RRH302 becomes strong enough to meet certain detectability criteria, e.g.,the synchronization signal (PSS/SSS) has an SNR above a certainthreshold or has a reference signal receive power (RSRP) above a certainother threshold, UE 300 may initialize the time/frequency tracking loopsusing the time/frequency offset information from the cell search forSCell RRH 302. UE 300 may also begin transmitting CQI information towireless network 30 through PCell eNB 301. Wireless network 30 may thenbe able to increase the bandwidth available to UE 300 by sending datathrough the secondary component carrier used by SCell RRH 302 inaddition to SCell access point 303.

FIG. 4 is a functional block diagram illustrating an example method 400including example blocks executed to implement one aspect of the presentdisclosure. At block 410, the method 400 may include monitoring adownlink radio link quality of a secondary cell operating in unlicensedspectrum at a mobile device for an event indicating failure of acommunication link over the secondary component carrier in theunlicensed spectrum with the secondary cell. In an aspect, for example,the monitoring component 332 of the UE 300 may monitor the downlinkradio link quality of a secondary cell (e.g., SCell access point 303)operating in unlicensed spectrum for an event that indicates failure ofthe communication link over the secondary component carrier in theunlicensed spectrum with the secondary cell. The monitoring component332 may perform the monitoring by various means, such as by periodicallyperforming a narrowband cell search for the secondary cell, countingnon-muted sub-frames from the secondary cell within a time period,monitoring determined CQI values for the secondary cell during a timeperiod, or monitoring an SNR metric associated with the secondary cell,and the like. For example, in an aspect, the monitoring component 332may perform periodic cell searches for the PSS/SSS of the secondarycell. These cell searches may be configured as narrowband searches inorder to detect the synchronization signals of the secondary cells, suchas the PSS and SSS.

In block 420, the method 400 may include detecting a first event basedon the downlink radio link quality. In an aspect, for example, theanalysis component 334 of the UE 300 may detect the first event based onthe downlink radio link quality. For example, the analysis component 334may determine that a failure event has occurred when the monitoringcomponent 332 detects a threshold number of consecutive search failures(e.g., searches where the PSS/SSS is not detected). The threshold may bea configurable number greater than or equal to two that indicating thatthe SCell is unavailable for a significant portion of time. A lowthreshold number may conserve resources by triggering a failure statefor the secondary cell, but may also prevent use of a secondary cellthat provides a number of opportunistic transmission opportunities. Inan aspect five consecutive search failures may indicate a lowavailability of the SCell suggesting a link failure event.

As another example, in an aspect, in block 410, the monitoring component332 may count a number of non-muted sub-frames received during a mostrecent time period or number of sub-frames. The monitoring component 332may determine whether each sub-frame is received based on an SNR of theCRS for the secondary cell. In block 420, when the number of sub-framesreceived during a time period is less than a threshold number ofsub-frames, the analysis component 334 may determine that a failureevent has occurred. In an aspect, the threshold may be based on a falsedetection rate for the CRS. For example, if due to random errors, the UEfalsely detects the CRS 1% of the time, the UE may determine that afailure event has occurred when the UE detects a CRS in less than 2%(indicating that about half of the detected sub-frames are falsedetections) of the sub-frames within a most recent time period.

As another example, in an aspect, the monitoring component 332 maymonitor determined CQI values in block 40. The UE 300 may includereported CQI values as well as values that are not reported, forexample, when the UE has no uplink data. Rather than looking for asingle low CQI value, which may be the result of a muted sub-frame, theanalysis component 334 may check for a threshold time period having nodetermined CQI with a non-zero value. If no non-zero CQI is determinedduring a time period, the analysis component 334 may determine that afailure event has occurred. The time period may be configurable. A timeperiod on the order of 1000 ms may be sufficient to detect a failureevent.

As another example, in an aspect, the monitoring component 332 maymonitor determined

SNR values in block 410. Rather than looking for a single low SNR value,which may be the result of a muted sub-frame, the analysis component 334may check for a threshold time period having no determined SNR with avalue less than an SNR threshold. For example, the SNR threshold may bean SNR necessary for meeting a minimum data rate (e.g., based on amodulation and coding scheme) that justifies the cost of monitoring thesecondary cell. If the determined SNR remains less than the SNRthreshold during a time period, the UE may determine that a failureevent has occurred. Once again, a time period on the order of 1000 msmay be sufficient to detect a failure event.

Additionally, any of the above failure events may be combined with anyof the other failure events. For example, the UE may monitor for all ofthe failure events and declare a local radio link failure when at leasttwo failure events have occurred. Accordingly, the method 400 mayoptionally include detecting a second failure event, detecting a thirdfailure event, and so on. In another aspect, one or more of the failureevents may be considered mandatory while other failure events areconsidered optional. For example, a UE may require one mandatory failureevent and another one of a plurality of other failure events to occur.Additionally, various thresholds may be set for the same failure eventsuch that, for example, a failure event based on a low level thresholdmay require a second failure event whereas a similar failure event basedon a higher level threshold may automatically trigger declaring a localradio link failure. The UE may use logic operations to combine thefailure events.

At block 430, the method 400 may include declaring a failure state ofthe secondary cell in response to detecting the first event. During thefailure state, the mobile device may adjust operation related to thesecondary component carrier. In an aspect, for example, the failurestate component 336 may declare a failure state of the secondary cell inresponse to detecting the first event. For example, when the analysiscomponent 334 detects a failure event in the connection or communicationlink with the secondary cell, the failure state component 336 may adjustvarious operations related to communication using the secondarycomponent carrier. For example, the failure state component 336 maysuspend or reduce the power or frequency of various components andresources associated with the secondary cell communication with thefailed communication link, such as the RF chip state, the transmit andreceive path states, the device voltage levels, memory usage, variouscomponents' operating frequencies, and the like. The failure statecomponent 336 may also suspend or deactivate the demodulation pathassociated with the failed secondary cell communication link. Thus, inresponse to the failure event detection, the failure state component 336may adjust communications operations to save power and resources.

In addition to deactivating various communications operations ondetection of a failure event, the UE may optionally attempt to recover asecondary connection. At block 440, the method 400 may optionallyinclude performing a cell search on the secondary component carrier inresponse to the failure state. For example, the UE 300 may beginmonitoring the periodic search results on secondary component carriersto check whether the secondary cell is found that meets certaindetectability criteria, e.g., the synchronization signal (PSS/SSS) hasan SNR above a certain threshold or has a RSRP above a certain otherthreshold for adequate communication. For example, the failure statecomponent 336 may control the monitoring component 332 to perform thesecell searches. These cell searches may be configured as narrowbandsearches in order to detect the synchronization signals of the secondarycells, such as the PSS and SSS. The UE may also begin maintenance of thefailure state with the wireless network by transmitting 0 CQI, signalinga rank indicator of 1 for the secondary cell, and, in case ofcross-carrier scheduling, the UE may cease signaling acknowledgements(ACKs) or negative ACKs (NACKs) for the downlink schedules of thesecondary cell.

At block 450, the method 400 may optionally include recovering thecommunication link over the secondary component carrier with one or moreconfigured secondary cells based on signal quality during the cellsearch. In an aspect, for example, the link recovery component 338 mayrecover the communication link over the secondary component carrier withthe one or more configured secondary cells based on signal qualityduring the cell search. For example, when one or more suitableconfigured secondary cells is detected during the optional cell searchperformed at block 440, the results from the search, such as thetime/frequency offsets, and the like, may be used to recover thecommunication link over the secondary component carrier with the one ormore configured secondary cells. The configured secondary cells mayinclude the secondary cell with which the previous communication linkwas lost, or it may be a different secondary cell enabled by the networkthat is detected and meets the appropriate threshold qualitymeasurements for establishing communication. On detection, the linkrecovery component 338 may update any secondary cell tracking loopsusing the offset data resulting from the cell search. This informationmay be used to initialize or re-initialize the tracking loops for theone or more configured secondary cells. Also upon detection of the oneor more configured secondary cells, the link recovery component 338 mayactivate any suspended or deactivated components or functionality thatwere suspended during the declared failure state, such as thedemodulation path, transmit and receive paths, and the like.

FIG. 5 is a timing diagram 500 illustrating an example of the operationof the UE 300 according to one aspect of the present disclosure. UE 300may operate in a wireless network that uses carrier aggregationincluding a secondary component carrier in unlicensed spectrum. At time501, the wireless network may configure the carrier aggregation,establishing the primary and secondary component carriers for UE 300. Attime 502, the wireless network may assign and may activate each of theSCells that will provide the secondary component carriers for UE 300.After activation of the SCells, UE 300 may establish a goodcommunication link with at least one of the SCells activated.Accordingly, after time 502, UE 300 may begin reporting CQI for theconnected SCell and may receive and demodulate data from this SCell,while maintaining the primary component carrier connection with theserving PCell. At time 503, UE 300 may detect a failure event with thecommunication link with at least one of the connected SCells.

In response to detecting the failure event, UE 300, at time 503, maydeclare a failure state with regard to the SCell and may modify variousoperations associated with secondary component carrier communicationwith the failed SCell, including suspending or reducing power to theSCell transmit and receive paths, the demodulation path, changing theoperating frequency of various components, and the like. In response todeclaring the failure state, UE 300 may also perform a narrowband searchfor the failed SCell link by monitoring the periodic search results onthe secondary component carrier to check whether the SCell is found andmeets certain detectability criteria, e.g., the synchronization signal(PSS/SSS) has an SNR above a certain threshold or has a RSRP above acertain other threshold.

During period 504, UE 300 may operate in a reduced power/resourceutilization state and may perform the narrowband cell search for thefailed SCell link. At time 505, UE 300 may again detect the SCellthrough the cell search. In response to detecting the SCell again, thesuspended components and/or operations may be reactivated for managingthe connection with the SCell. UE 300, thus, may begin reporting CQI forthe SCell and receiving and decoding data from the SCell.

FIG. 6 is a block diagram illustrating a UE 300 configured according toone aspect of the present disclosure. UE 300 may include thecontroller/processor 280 (see FIG. 2). Controller/processor 280 maycontrol the components and may execute logic stored in memory 282 (seeFIG. 2) that provides the features of functionalities of UE 300including the features and functionalities of radio link statuscomponent 330. For example, the radio link status component 330 mayinclude logic stored in memory 282. In order to monitor thecommunication link with the connected SCell, UE 300, under control ofcontroller/processor 280, may control the signals received through theSCell demodulation path 603 of wireless radios 604, from the connectedSCell. The combination of these components and acts may provide meansfor monitoring a downlink radio link quality of one or more secondarycells at a mobile device for an event indicating failure of acommunication link with at least one of the one or more secondary cells.

Controller/processor 280 may access memory 282 to execute link analysislogic 600. The executing environment of link analysis logic 600, mayanalyze the connection with the SCell and may determine whether a linkfailure has occurred. For example, the executing link analysis logic 600may cause controller/processor 280 to periodically execute cell searchlogic 607 in memory 282 to perform a cell search for the active SCelllink by monitoring the periodic search results on the secondarycomponent carrier to check whether the SCell is found. UE 300 mayreceive the search results after executing cell search logic 607, undercontrol of controller/processor 280, and receiving and sending searchsignals through SCell transmit path 602 and SCell demodulation path 603,respectively, in wireless radios 604. The controller/processor 280 maydeclare a failure event when the SCell is not found in the periodicsearch results for a threshold number of consecutive searches.

Alternatively, the executing link analysis logic 600 may causecontroller/processor 280 to detect the failure event when a number ofsub-frames successfully received is less than a threshold number ofsub-frames. The SCell demod path 603 may determine whether a sub-frameis successfully received based on whether a CRS of the SCell is detectedin the sub-frame.

In another aspect, the executing link analysis logic 600 may cause thecontroller/processor 280 to monitor a channel quality indication (CQI)determined by the SCell demodulation path 603 and detect the failureevent when no CQI value greater than 0 is determined during a timeperiod.

In another aspect, the executing link analysis logic 600 may causecontroller/processor 280 to determine the SNR of the SCell signalreceived at wireless radios 604 through SCell demodulation path 603 andwhen the SNR remains below a predetermined threshold for a certainperiod of time, the UE 300 may declare the failure state.

Based on the results of the executing link analysis logic 600,controller/processor 280 may detect a failure of the communication linkwith the SCell and may declare a failure state. In response, to thedeclared failure state, UE 300, under control of controller/processor280, may suspend or deactivate SCell transmit path 602 and SCelldemodulation path 603 in wireless radios 604. Controller/processor 280may also reduce the power output of power supply 605 in order to reducethe voltage level to wireless radios 604, and the like. Moreover,controller/processor 280 may change the frequency of various componentsby changing the operations of frequency generator 606. The combinationof these components and acts may provide means for declaring a failurestate on the at least one of the one or more secondary cells in responseto detecting the event, during which mobile device may adjust operationrelated to the secondary component carrier

Also, in response to the declared failure state, controller/processor280 may execute cell search logic 607 in memory 282 to perform a cellsearch for the failed SCell link by monitoring the periodic searchresults on the secondary component carrier to check whether the SCell isfound and meets certain detectability criteria, e.g., thesynchronization signal (PSS/SSS) has an SNR above a certain threshold orhas a RSRP above a certain other threshold. The executing cell searchlogic 607 sends search messages and listens for synchronization signalsover wireless radios 604. The combination of these components and actsmay provide means for performing cell search for the at least one of theone or more secondary cells in response to the failure state.

During the declared failure state, UE 300 may also begin transmitting alow, e.g., a 0, CQI and signaling a low, e.g., a 1, rank indicator forthe SCell to the network. In case of cross-carrier scheduling, UE 300may also cease signaling acknowledgements (ACKs) or negative ACKs(NACKs) for the downlink schedules of the SCell.

When the SCell is detected by UE 300, through execution of cell searchlogic 607 by controller/processor 280, controller/processor 280 mayreactivate each of the components and processes that were suspendedduring the failure state. Controller/processor 280 may reactivate SCelltransmit path 602 and SCell demodulation path 603, and may return thepower and frequency settings back to the original levels through accessto power supply 605 and frequency generator 606. Controller/processor280 may compare the time/frequency offsets that resulted from executionof cell search logic 607 to the operation of SCell tracking loops 601operated from SCell demodulation path 603 by controller/processor 280.If the time/frequency offsets determined in the cell search do not matchthe time/frequency offsets of the operating SCell tracking loops 601,and the difference is greater than the pull-in range of the operatingSCell tracking loops 601, then controller/processor 280 may initializeor re-initialize SCell tracking loops 601 using the time/frequencyoffsets from execution of cell search logic 607. UE 300, under controlof controller/processor 280 may then be able to recover or reestablishthe connection with the detected SCell. UE 300 may begin transmittingCQI for the recovered SCell to the network and may begin to receive datatransmitted over the SCell to increase the throughput from the network.The combination of these components and acts may provide means forrecovering the communication link with a secondary cell detected duringthe cell search. Referring to FIG. 7, one or more components of UE 300of FIG. 3, by which radio link monitoring of secondary cells inunlicensed spectrum may be implemented according to an aspect of thedisclosure, are illustrated with respect to radio link status component330. It should be noted that each of the one or more components of UE300 may be implemented as software, hardware, firmware, or anycombination thereof. As noted above, UE 300 generally operates radiolink status component 330 to monitor the status of communication link136 and to declare a failure state when a failure event is detected suchthat the UE 300 may consume less power.

According to the present aspects, the UE 300 may include one or moreprocessors 733 that may operate in combination with the radio linkstatus component 330 configured to monitor the status of communicationlink 136 and to declare a failure state when a failure event isdetected. For example, the processors 733 may include thecontroller/processor 280 of FIG. 2 and FIG. 6. The radio link statuscomponent 330 may be communicatively coupled to a transceiver 740, whichmay include a receiver 742 for receiving and processing RF signals and atransmitter 744 for processing and transmitting RF signals. Theprocessor 733 may be coupled to the transceiver 740 and a memory 730 viaat least one bus 760. The memory 730 may correspond to the memory 282 inFIG. 2 and FIG. 6.

The receiver 742 may include hardware, firmware, and/or software codeexecutable by a processor for receiving data, the code comprisinginstructions and being stored in a memory (e.g., computer-readablemedium). The receiver 742 may be, for example, a radio frequency (RF)receiver. In an aspect, the receiver 742 may receive signals transmittedby one or more of the eNBs 110. In an aspect, the receiver 742 may beconfigured to receive signals from the eNB 110 as a secondary cell.

The transmitter 744 may include hardware, firmware, and/or software codeexecutable by a processor for transmitting data, the code comprisinginstructions and being stored in a memory (e.g., computer-readablemedium). The transmitter 744 may be, for example, a RF transmitter. Thetransmitter 744 may transmit information regarding the communicationlink 136 such as a CQI.

In an aspect, the one or more processors 733 can include a modem 738that uses one or more modem processors. The various functions related toradio link status component 330 may be included in modem 738 and/orprocessors 733 and, in an aspect, can be executed by a single processor,while in other aspects, different ones of the functions may be executedby a combination of two or more different processors. For example, in anaspect, the one or more processors 733 may include any one or anycombination of a modem processor, or a baseband processor, or a digitalsignal processor, or a transmit processor, or a transceiver processorassociated with transceiver 740. In particular, the one or moreprocessors 733 may implement components included in the radio linkstatus component 330.

Moreover, in an aspect, UE 300 may include RF front end 750, which mayoperate in communication with one or more antennas 720 and transceiver740 for receiving and transmitting radio transmissions, for example,wireless communications transmitted by at least one eNB 110 or wirelesstransmissions transmitted by UE 300. RF front end 750 may be connectedto one or more antennas 720 and can include one or more low-noiseamplifiers (LNAs) 751, one or more switches 752, 753, 756, one or morepower amplifiers (PAs) 755, and one or more filters 754 for transmittingand receiving RF signals. In an aspect, the wireless radios 604 andcomponents thereof in FIG. 6 may include or may be implemented by the RFfront end 750.

In an aspect, LNA 751 can amplify a received signal at a desired outputlevel. In an aspect, each LNA 751 may have a specified minimum andmaximum gain values. In an aspect, RF front end 750 may use one or moreswitches 752 to select a particular LNA 751 and its specified gain valuebased on a desired gain value for a particular application.

Further, for example, one or more PA(s) 755 may be used by RF front end750 to amplify a signal for an RF output at a desired output powerlevel. In an aspect, each PA 755 may have specified minimum and maximumgain values. In an aspect, RF front end 750 may use one or more switches756 to select a particular PA 755 and its specified gain value based ona desired gain value for a particular application.

Also, for example, one or more filters 754 can be used by RF front end750 to filter a received signal to obtain an input RF signal. Similarly,in an aspect, for example, a respective filter 754 can be used to filteran output from a respective PA 755 to produce an output signal fortransmission. In an aspect, each filter 754 can be connected to aspecific LNA 751 and/or PA 755. In an aspect, RF front end 750 can useone or more switches 753 to select a transmit or receive path using aspecified filter 754, LNA 751, and/or PA 755, based on a configurationas specified by transceiver 740 and/or processor 733.

The monitoring component 332 may include hardware, firmware, and/orsoftware code executable by a processor (e.g., processor(s) 733) formonitoring a downlink radio link quality of a secondary cell inunlicensed spectrum, the code comprising instructions and being storedin a memory (e.g., memory 730 or another computer-readable medium). Forexample, the monitoring component 332 may include or control an antenna720, RF front end 750, and/or receiver 742 to receive signalstransmitted by the eNB on communication link 136. The monitoringcomponent 332 may monitor various properties of the communication linkand may store information regarding the communication link 136 for atime period. For example, the monitoring component 332 may monitor:received sub-frames including a CRS, CQI values determined for thecommunication link 136, and/or SNR values determined for thecommunication link 136. The monitoring component 332 may also performperiodic cell searches for a synchronization signal of the eNB 110 anddetermine whether the synchronization signal is detected during eachsearch.

The analysis component 334 may include hardware, firmware, and/orsoftware code executable by a processor (e.g., processor(s) 733) fordetecting a first event based on the downlink radio link quality, thecode comprising instructions and being stored in a memory (e.g., memory730 or another computer-readable medium). For example, the analysiscomponent 334 may include configurable thresholds stored in the memory730 and instructions executable by the processor 733 for determiningwhen the downlink radio link quality indicates a radio link failureevent.

The failure state component 336 may include hardware, firmware, and/orsoftware code executable by a processor (e.g., processor(s) 733) fordeclaring a failure state of the secondary cell in response to detectingthe first event, during which the UE 300 adjusts operation related tothe secondary component carrier in the unlicensed spectrum, the codecomprising instructions and being stored in a memory (e.g., memory 730or another computer-readable medium). In an aspect, the failure statecomponent 336 may control various components of the UE 300 to reducepower consumption during the failure state. For example, the failurestate component 335 may control the antenna 720, RF front end 750,and/or receiver 742 to stop attempting to receive or decode signalstransmitted by the eNB on communication link 136 during the failurestate.

The link recovery component 338 may include hardware, firmware, and/orsoftware code executable by a processor (e.g., processor(s) 733) forattempting to recover from a radio link failure state, the codecomprising instructions and being stored in a memory (e.g., memory 730or another computer-readable medium). For example, the link recoverycomponent 338 may control the antenna 720, RF front end 750, and/orreceiver 742 to perform a cell search for the failed SCell link bymonitoring the periodic search results on the secondary componentcarrier to check whether the SCell is found and meets certaindetectability criteria. The link recovery component 338 may thenreactivate the SCell and end the failure state of the secondary cell.

FIG. 8 illustrates a conceptual diagram 800 showing an example ofcarrier aggregation using a component carrier in unlicensed spectrum.For example, the UE 300 may perform carrier aggregation. In an aspect,unlicensed spectrum may refer to a portion of frequency spectrum that isnot licensed (e.g., by a regulatory agency such as the FederalCommunications Commission (FCC)) to a particular licensee. For example,a large portion (e.g., >400 MHz) of spectrum may be available in a 5 GHzband while another portion of unlicensed spectrum may be available in a2.4 GHz band. In an aspect, other radio access technologies (e.g.,Wi-Fi) may also use the unlicensed spectrum. As illustrated in FIG. 8,LTE in unlicensed spectrum may utilize a primary component carrier inlicensed spectrum and a secondary component carrier in unlicensedspectrum. The primary component carrier may be an LTE-Advanced anchorthat provides for mobility and other signaling. A network source 810such as a packet data network gateway may provide downlink data to PCell820 for transmission over the primary component carrier 822 and to anSCell 830 for transmission over the secondary component carrier 832. TheUE 300 including a radio link status component 330 may aggregate thebandwidth of the component carriers at the media access control (MAC)layer to increase throughput. The radio link status component 330 maymonitor the status of the communication link on the secondary componentcarrier 832, which may be in unlicensed spectrum. LTE in unlicensedspectrum may include features for coexistence with neighbor systems suchas Wi-Fi.

FIG. 9 illustrates a timing diagram 900 showing an example of carriersense adaptive transmission (CSAT) for use in unlicensed spectrum. CSATis a mechanism to reduce co-channel interference from LTE in unlicensedspectrum to Wi-Fi. CSAT may be implemented when no free channel (notused by Wi-Fi) is available. CSAT may create a time division multiplex(TDM) transmission pattern on an SCell with a cycle, T_(CSAT) 910. Asillustrated in FIG. 9, a MAC control element at an eNB may use fastactivation/deactivation to switch the SCell between an on period(T_(ON)) 920 and an off period (T_(OFF)) 930. The SCell may obtainmeasurement during the T_(OFF) 930 of Wi-Fi medium utilization. TheSCell may use a co-located Wi-Fi access point to sniff the medium usingpreamble detection for Wi-Fi activity. The T_(CSAT) or the T_(ON) andT_(OFF) periods may be adjusted based on the Wi-Fi activity. Asdiscussed above, when CSAT is implemented, the UE may have difficultymonitoring radio link quality because it may difficult to determinewhether the sub-frame was muted or the radio link was poor quality. Theradio link failure events discussed above, however, may be accuratelydetected even when the UE is unsure of whether a sub-frame was muted.

FIG. 10 illustrates a timing diagram 1000 showing an example of anenhanced CSAT (eCSAT) system that may operate without a clear channelassessment (CCA) or listen before talk (LBT) procedure. The eNB mayactivate UEs with downlink data via an activation MAC control element(CE) command and may deactivate UEs without downlink data via adeactivation MAC CE command to form an outer loop control 1010. The eNBmay run an inner activation/deactivation cycle by turning the CRS on oroff. The UE may assume the cell is on when CRS is present in asub-frame. The UE may assume the cell is off when CRS is not present inthe subframe. When in an OFF-state, the SCell may cease alltransmissions including PSS/SSS, scheduling information (SI) signals,CRS signals, etc. A continuous on duration may be expected to be shorterthan the T_(ON) in CSAT. For example, the on duration (T_(on)) 1020 maybe approximately 4 ms, although 1 ms is theoretically possible. Asillustrated in FIG. 10, the UE may activate the outer loop control 1010on the 8 ^(th) sub-frame after the activation command sub-frame and theSCell may start a duty cycle including an on/off pattern for that UE.The SCell may maintain the duty cycle based on observation of channelactivity. The UE may stop monitoring downlink sub-frames after receivingthe deactivation command.

In an aspect, the eNB may also transmit a discovery reference signal(DRS) 1030, which may include physical layer signals such as a primarysynchronization signal (PSS), secondary synchronization signal (SSS),and a cell specific reference signal (CRS). As illustrated in FIG. 10,the DRS 1030 may not be time aligned with the T_(ON) period.Accordingly, the DRS and component signals may be muted. Because the UEmay detect the state of the SCell based on the CRS signals, monitoringradio link quality may be difficult because it may be unclear whetherCRS in a sub-frame was intentionally muted or whether the quality of theCRS was poor. Once again, the radio link failure events discussed abovemay be accurately detected even when the UE is unsure of whether asub-frame was muted.

FIG. 11 illustrates a timing diagram 1100 showing an example of eCSAToperation with a CCA or LBT procedure. The eCSAT operation may operateas in FIG. 10, but the SCell may also perform a CCA operation 1110before the inner activation to turn the CRS on. The CCA operation mayensure that the channel is clear of Wi-Fi or other transmissions beforean LTE transmission begins. Further, the SCell may transmit a clear tosend to self (CTS2S) message 1120 immediately following the CCAoperation. The CTS2S transmission may silence Wi-Fi systems for aduration. The eCSAT operation, however, may not provide certainty at theUE as to whether CRS in a sub-frame was intentionally muted or whetherthe quality of the CRS was poor. Once again, the radio link failureevents discussed above may be accurately detected even when the UE isunsure of whether a sub-frame was muted.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

The functional blocks and modules in FIG. 4 may comprise processors,electronics devices, hardware devices, electronics components, logicalcircuits, memories, software codes, firmware codes, etc., or anycombination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure. Skilled artisans will also readilyrecognize that the order or combination of components, methods, orinteractions that are described herein are merely examples and that thecomponents, methods, or interactions of the various aspects of thepresent disclosure may be combined or performed in ways other than thoseillustrated and described herein.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. A computer-readable storage medium may be anyavailable media that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM orother optical disk storage, magnetic disk storage or other magneticstorage devices, or any other medium that can be used to carry or storedesired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, non-transitory connections may properly be includedwithin the definition of computer-readable medium. For example, if theinstructions are transmitted from a website, server, or other remotesource using a coaxial cable, fiber optic cable, twisted pair, ordigital subscriber line (DSL), then the coaxial cable, fiber opticcable, twisted pair, or DSL are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communication on asecondary component carrier in unlicensed spectrum in a wirelesscommunication network using carrier aggregation, comprising: monitoringa downlink radio link quality of a secondary cell in the unlicensedspectrum at a mobile device for an event indicating failure of acommunication link over the secondary component carrier in theunlicensed spectrum with the secondary cell; detecting a first eventbased on the downlink radio link quality; and declaring a failure stateof the secondary cell in response to detecting the first event, duringwhich the mobile device adjusts operation related to the secondarycomponent carrier in the unlicensed spectrum.
 2. The method of claim 1,wherein monitoring the downlink radio link quality of the secondary cellin the unlicensed spectrum includes determining, for each of a pluralityof sub-frames, whether the sub-frame includes a cell specific referencesignal (CRS).
 3. The method of claim 2, wherein detecting the firstevent includes detecting the first event based on sub-frames determinedto include the CRS.
 4. The method of claim 1, wherein monitoring thedownlink radio link quality of the secondary cell includes performing acell search for a synchronization signal of the secondary cell in theunlicensed spectrum at the mobile device, and wherein detecting thefirst event includes determining that the synchronization signal is notdetected in a threshold number of consecutive cell searches.
 5. Themethod of claim 1, wherein monitoring the downlink radio link quality ofthe secondary cell includes determining a number of sub-frames includinga cell specific reference signal (CRS) received from the secondary cellduring a period of most recent sub-frames, and wherein detecting thefirst event includes determining that the number of sub-frames includingthe CRS is less than a threshold number of sub-frames.
 6. The method ofclaim 5, wherein a ratio between the threshold number of sub-frames anda number of sub-frames in the period is based on a false detection ratefor the CRS.
 7. The method of claim 1, wherein monitoring the downlinkradio link quality of the secondary cell includes monitoring a channelquality indication (CQI) determined by the mobile device, and whereindetecting the first event includes determining that no CQI value greaterthan 0 is determined during a time period.
 8. The method of claim 1,wherein monitoring the downlink radio link quality of the secondary cellincludes monitoring a signal-to-noise ratio (SNR) value at the mobiledevice, and wherein detecting the first event includes determining thatthe SNR value does not exceed a threshold value during a time period. 9.The method of claim 1, further comprising: detecting a second eventbased on the downlink radio link quality, wherein declaring the failurestate of the secondary cell is in response to detecting both the firstevent and the second event.
 10. The method of claim 9, wherein the firstevent is a mandatory event and the second event is one of two or moreoptional events.
 11. An apparatus for wireless communication on asecondary component carrier in unlicensed spectrum in a wirelesscommunication network using carrier aggregation, the apparatuscomprising: at least one processor; and a memory coupled to the at leastone processor, wherein the at least one processor is configured to:monitor a downlink radio link quality of a secondary cell operating inthe unlicensed spectrum at a mobile device for an event indicatingfailure of a communication link over the secondary component carrierwith the secondary cell; detect a first event based on the downlinkradio link quality; and declare a failure state of the secondary cell inresponse to detecting the first event, during which the mobile deviceadjusts operation related to the secondary component carrier in theunlicensed spectrum.
 12. The apparatus of claim 11, wherein the at leastone processor is configured to monitor the downlink radio link qualityof the secondary cell in the unlicensed spectrum by determining, foreach of a plurality of sub-frames, whether the sub-frame includes a cellspecific reference signal (CRS).
 13. The apparatus of claim 12, whereinthe at least one processor is configured to detect the first event basedon sub-frames determined to include the CRS.
 14. The apparatus of claim11, wherein the at least one processor is configured to monitor thedownlink radio link quality of the secondary cell in the unlicensedspectrum by performing a cell search for a synchronization signal of thesecondary cell in the unlicensed spectrum at the mobile device, andwherein the at least one processor is configured to detect the firstevent when the synchronization signal is not detected in a thresholdnumber of consecutive cell searches.
 15. The apparatus of claim 11,wherein the at least one processor is configured to monitor the downlinkradio link quality of the secondary cell in the unlicensed spectrum bydetermining a number of sub-frames including a cell specific referencesignal (CRS) received from the secondary cell during a period of mostrecent sub-frames, and wherein the at least one processor is configuredto detect the first event when the number of sub-frames including theCRS is less than a threshold number of sub-frames.
 16. The apparatus ofclaim 15, wherein a ratio between the threshold number of sub-frames anda number of sub-frames in the period is based on a false detection ratefor the CRS.
 17. The apparatus of claim 11, wherein the at least oneprocessor is configured to monitor the downlink radio link quality ofthe secondary cell in the unlicensed spectrum by monitoring a channelquality indication (CQI) determined by the mobile device, and whereinthe at least one processor is configured to detect the first event whenno CQI value greater than 0 is determined during a time period.
 18. Theapparatus of claim 11, wherein the at least one processor is configuredto monitor the downlink radio link quality of the secondary cell in theunlicensed spectrum by monitoring a signal-to-noise ratio (SNR) value atthe mobile device, and wherein the at least one processor is configuredto detect the first event when the SNR value does not exceed a thresholdvalue during a time period.
 19. The apparatus of claim 11, wherein theat least one processor is configured to detect a second event based onthe downlink radio link quality, and wherein the at least one processoris configured to declare the failure state of the secondary cell inresponse to detecting both the first event and the second event.
 20. Theapparatus of claim 19, wherein the first event is a mandatory event andthe second event is one of a plurality of optional events.
 21. Anapparatus for wireless communication on a secondary component carrier inunlicensed spectrum in a wireless communication network using carrieraggregation, comprising: means for monitoring a downlink radio linkquality of a secondary cell operating in the unlicensed spectrum at amobile device for an event indicating failure of a communication linkover the secondary component carrier with the secondary cell; means fordetecting a first event based on the downlink radio link quality; andmeans for declaring a failure state of the secondary cell in response todetecting the event, during which the mobile device adjusts operationrelated to the secondary component carrier in the unlicensed spectrum.22. The apparatus of claim 21, wherein the means for monitoring areconfigured to monitor the downlink radio link quality of the secondarycell in the unlicensed spectrum by determining, for each of a pluralityof sub-frames, whether the sub-frame includes a cell specific referencesignal (CRS).
 23. The apparatus of claim 22, wherein the means fordetecting are configured to detect the first event based on sub-framesdetermined to include the CRS.
 24. The apparatus of claim 21, whereinthe means for monitoring are configured to perform a cell search for asynchronization signal of the secondary cell in the unlicensed spectrumat the mobile device, and wherein the means for detecting are configuredto detect the event when the synchronization signal is not detected in athreshold number of consecutive cell searches.
 25. The apparatus ofclaim 21, wherein the means for monitoring are configured to determine anumber of sub-frames including a cell specific reference signal (CRS)received from the secondary cell during a period of most recentsub-frames, and wherein the means for detecting are configured to detectthe event when the number of sub-frames including the CRS is less than athreshold number of sub-frames.
 26. The apparatus of claim 25, wherein aratio between the threshold number of sub-frames and a number ofsub-frames in the period is based on a false detection rate for the CRS.27. The apparatus of claim 21, wherein the means for monitoring areconfigured to monitor a channel quality indication (CQI) determined bythe mobile device, and wherein the means for detecting are configured todetect the first event when no CQI value greater than 0 is determinedduring a time period.
 28. The apparatus of claim 21, wherein the meansfor monitoring are configured to monitor a signal-to-noise ratio (SNR)value at the mobile device, wherein the means for detecting areconfigured to detect the event when the SNR value does not exceed athreshold value during a time period.
 29. A non-transitorycomputer-readable medium storing computer executable code for wirelesscommunication on a secondary component carrier in unlicensed spectrum ina wireless communication network using carrier aggregation, comprisingcode for causing a computer to: monitor a downlink radio link quality ofa secondary cell operating in the unlicensed spectrum at a mobile devicefor an event indicating failure of a communication link over thesecondary component carrier with the secondary cell; detect a firstevent based on the downlink radio link quality; and declare a failurestate of the secondary cell in response to detecting the first event,during which the mobile device adjusts operation related to thesecondary component carrier in the unlicensed spectrum.
 30. Thenon-transitory computer-readable medium of claim 29, wherein detectingthe first event includes detecting one or more of: a synchronizationsignal is not detected in a threshold number of consecutive cellsearches; a number of sub-frames including a cell specific referencesignal (CRS) received from the secondary cell during a period of mostrecent sub-frames is less than a threshold number of sub-frames; nochannel quality indication (CQI) value determined by the mobile devicegreater than 0 is determined during a time period; or a signal-to-noiseratio (SNR) value at the mobile device does not exceed a threshold valueduring the time period.